Binary electromagnetic indicators providing non-illuminated contrasting color indicia are known by those skilled in the art and find utility in a variety of installations, e.g., aircraft, portable electronic equipment, computers, etc. Such indicators are often preferred over illuminated indicators as, for example, those using glow tubes or bulbs where the ambient light conditions make it difficult to distinguish the display from the surrounding background. Electromagnetic indicators are also preferred for installations that are subject to shock or where changes in ambient temperature are significant enough to accelerate deterioration of glow tubes and the like.
Illustrative prior art forms of binary electromagnetic indicators are disclosed in U.S. Pat. No. 704,462 to Pihl and U.S. Pat. No. 4,115,769 to Hart et al. These patents each disclose an electromagnetic indicator which is responsive to a fault or malfunction condition, whereby one of a pair of cooperating indicator members, each of which is disc-shaped and mounted along a common axis, rotates relative to the other to change a visual display. Both of the indicator members have a plurality of sectors of like size. The sectors of the stationary indicator member are alternately transparent and opaque, while the sectors of the movable indicator member are totally opaque although alternately distinguishable. In these patents the alternate sectors of the movable indicators are white and dark and the opaque sectors of the stationary indicator member are also dark. For example, the dark sectors of both indicator members may be colored with a black paint. Thus, in one position, the "set" position, the black sectors of the movable indicator member align with black sectors of the stationary indicator member and the white sectors of the movable indicator member align with transparent sectors of the stationary indicator member. In the position to which the movable indicator member moves as a result of a fault or malfunction condition, the opposite alignment will be seen. An alignment of the sectors of the movable indicator member also may be employed such that in the " set" position its black sectors align with the transparent sectors of the stationary indicator member.
U.S Pat. No. 4,652,868 to Hart discloses an indicator responsive to a fault signal in a monitored channel which provides an indication of the occurrence of a fault and an electrical interface to assure that the indicator will respond to the fault signal even if the fault signal is of an extremely short time duration. Either a single indicator or a plurality of indicators to respond to a plurality of channels to be monitored may be controlled by the electrical interface that functions to respond to an input fault signal and latch that signal for the duration of time required to permit the indicator to indicate the fault. The latch which may function as an AND gate provides a continuous enabling voltage output. A switch in the form of a transistor array, activated by an output of the latch, permits current to flow from a source, through a "set" coil of the indicator, to energize the particular indicator and provide a fault indication for the channel being monitored. The electrical interface also includes a circuit to "reset" the indicator and to "reset" the latch that shall have responded to the fault signal.
Known electromagnetic indicators have been found to suffer from a number of disadvantages. These disadvantages relate to the complexity of structure, the costs of fabrication, magnetic flux leakage as well as the physical size of the device and the degree of precision to which various components must be manufactured.
The above-described prior art devices as well as numerous other known devices employ an electromagnet which is energized by an electrical signal such as a fault signal. Such an electromagnet typically comprises a rigid fixed core and a wire wound coil which is formed by winding a wire or wires onto the rigid fixed core. Alternatively, wire may be wound onto a bobbin which is subsequently inserted onto a central rigid fixed core. The rigid fixed core may take on a wide variety of configurations such as a straight rod member, a U-shaped member, a C-shaped member, an L-shaped member, etc. However, regardless of the specific configuration, it is desirable to minimize flux leakage while producing high ampere turns and low operational power. In an illustrative magnetic system comprising a stationary C-shaped electromagnet having poles at each of its two ends and a rotor mounted so as to rotate within the area between the two pole pieces, magnetic flux leakage may be minimized by decreasing the air gap between the rotor and the pole pieces. Moreover, magnetic flux leakage can generally be minimized and efficiency increased by decreasing air gaps in magnetic circuits, whether the magnetic circuit is part of a motor or not.
Unfortunately, in order to decrease such air gaps, the pole piece or pieces must physically be in a very close relationship with any other element defining the air gap. In practice, however, this is not easy to achieve due to imprecise manufacturing tolerances which may lead to excessive air gaps or to direct physical contact between stationary pole pieces and a rotating member, especially in the case of C-shaped and U-shaped electromagnets. Furthermore, it is desirable, from a manufacturing point of view, to provide a single electromagnet which could be used in a wide variety of magnetic circuits to take advantage of the individual magnetic circuit configurations and reduce flux leakage.
Another disadvantage of prior art devices relates to the difficulty associated with winding wire onto rigid fixed cores which are not simple straight rod members. For example, it is often desirable to construct a horseshoe or U-shaped electromagnet by winding wire onto a U-shaped rigid fixed core. Unfortunately, in practice this is quite difficult to accomplish manually and even more difficult, if not impossible, to accomplish automatically by automatic wire winding machines. As a result, U-shaped electromagnets are sometimes only wound with wire along a straight section of the U-shaped member. However, this is also difficult and unnecessarily limits the amount of magnetic flux obtainable from the U-shaped member.
A further disadvantage of prior art devices relates to the loss of magnetic flux due to the staking together of structural members to create the C-shaped, L-shaped, U-shaped, etc. rigid fixed cores. Such structural members are generally staked together by rivets or similar fastening means, leading to a leakage of magnetic flux which could otherwise be beneficially employed. Although staking together of structural members after one or some of the members have been wound with wire may solve the problem of winding wire on the entire curved rigid core, this process unfortunately results in increased magnetic flux loss.